The present invention relates to disposable devices for the collection, transport, and storage of a specimen prior to analysis for a component thereof, and specifically to an integral feature which provides for convenient removal of a sample of the collected specimen. The present invention also relates to assays for soluble components in colored or opaque semi-solid specimens, and specifically to a method for obtaining a liquid sample from such specimens.
The collection, transportation and storage of many types of specimens for delayed routine analysis requires appropriate and efficient packaging systems. Packages for specimens of potentially infectious clinical biological materials sent through the mails should be lightweight, sealable, unbreakable, and disposable. Further, removing samples from the packaged specimens must be accomplished with as little handling as possible to avoid contamination.
Further, the chemical detection of soluble components in the liquid phase of semi-solid specimens can be difficult if the liquid phase is not first isolated. Common qualitative colorimetric tests cannot be used because a positive test result can be obscured by the opaque, colored material of the specimen. At the same time, however, conventional isolation procedures are impractical in the case of routine medical tests which must be processed economically. Therefore special methods have been developed to analyze these specimens intact, without first extracting a liquid sample.
Specimens of fecal material are commonly collected and mailed to a commercial laboratory for analysis for occult blood. This type of specimen is a paradigm of the specimen collecting and analysis difficulties indicated. A number of fecal occult blood test systems use disposable, sealable collecting devices suitable for storage and transport of a fecal specimen preliminary to the analysis for hemoglobin. These tests usually incorporate a reagent for the guaiac test, capable of detecting hemoglobin in an intact fecal specimen. Guaiac chemistry is based on the ability of hemoglobin present in blood to act as a peroxidase, releasing O.sub.2 from peroxide to change the color of an indicating guaiacum resin to a blue color.
U.S. Pat. No. 4,225,557 to Hartl discloses a typical physical design for an occult blood test, which provides an area having an absorbent surface and impregnated with guaiac, mounted within a frame on a rigid panel of a folder, onto which a fecal specimen is applied. After the specimen is collected, a flap of the folder covers the absorbent surface and seals. At this point, the system is stable, and the device may be taken or mailed to a laboratory, where the test for hemoglobin is performed. To test for the presence of hemoglobin, a few drops of hydrogen peroxide are applied to the exposed underside of the absorbent layer. The peroxide passes through to react with any hemoglobin present in the specimen, and in a positive test, the guaiac in the absorbent layer is converted to a blue color. The color is conveniently observed, free of interference by the opaque, colored specimen, on the same underside of the absorbent layer.
This form of the test has a number of defects and they have been met by a series of modifications and improvements. First, guaiac is easily oxidized to a blue color on prolonged exposure to air. Therefore, it must be protected from oxidation in order to prevent incorrect results, and its effectiveness verified at the time the assays are performed. U.S. Pat. No. 4,382,064 to Detwieler et al. discloses a coating for surfaces in contact with guaiac in the device, the coating comprising the antioxidant BHT incorporated into a varnish applied to the surfaces. U.S. Pat. No. 4,365,970 to Laurence et al. discloses on-slide positive and negative performance monitors for the guaiac test wherein the positive control comprises a hemoglobin component.
Another defect in the guaiac test for occult blood is that it is subject to interference from other oxidative reactions in the specimen which give rise to false positive results. One source is that of peroxidases present in foods which apparently survive the digestive process and remain active in fecal material. U.S. Pat. No. 4,333,734 to Fleischer discloses an improved guaiac chemistry which comprises inhibitors of competing peroxidases. Another is that of oxidizing agents used to clean toilet bowls from which the specimens are usually retrieved, and U.S. Pat. No. 4,675,160 to Talmage et al. discloses test controls to detect this source of interference.
Another problem is that these tests do not provide for reproducible sampling. For even qualitative tests to be reliable and significant from test to test, they should be carried out on a defined, preferably constant, specimen volume. U.S. Pat. No. 4,273,741 to Levine discloses a constant volume stool testing device wherein the specimen is applied to a surface containing an area which is a recessed grid. That portion of specimen remaining above the grid is removed before the test is performed.
The consequences of a false positive occult blood test, indicating colo-rectal bleeding, are serious since it requires the consideration of more serious invasive diagnostic procedures. For this reason, it is customary to confirm a positive occult blood test with a more specific test for hemoglobin. To verify the test results independently, for example, by immunoassay for hemoglobin, it is often necessary to secure a sample of the fluid phase of the specimen, substantially uncontaminated by solid material.
One occult blood testing device provides for a guaiac test for hemoglobin together with simultaneous sampling of a liquid filtrate of the fecal specimen. U.S. Pat. No. 4,645,743 to Baker discloses a fecal testing device comprising an absorbent specimen pad having a pocket in which is inserted a second liquid sampling sheet. The specimen pad can be inserted and mounted in a rigid frame which comprises a sample receiving sheet impregnated with guaiac. After a fecal specimen is deposited on the absorbent pad, it is placed, specimen side down, in the frame against the receiving sheet. The guaiac test is performed in the conventional way, by applying a few drops of peroxide on the underside of the receiving sheet. The second sampling layer, the insert, receives a liquid portion of the fecal specimen which has filtered inwardly from the absorbent pad. The insert, containing the liquid sample, can be removed and cut into portions from which the retained liquid can be eluted and assayed by any desired procedure, for example, a radioimmunoassay.
Methods similar to the Baker device for follow-up or supplementary testing are unsatisfactory in a number of ways, and can lead to incorrect results.
First, a liquid sample which has been filtered through a volume of an absorbent pad may be less concentrated and its composition not representative of the original liquid sample. Absorbent material exerts an initial chromatographic effect on the solutions passing through it, retarding the passage of large molecules with respect to smaller molecules, particularly those of water. Unless the total volume of the liquid in the specimen is sufficient to saturate the pad and thus overcome this effect, the filtered liquid sample will be diluted and its relative composition distorted by the extraction of larger molecules. The liquid content which will flow from most semi-solid biological specimens is usually quite limited. The effect of collecting a small volume of filtered liquid therefrom through an absorbent pad in almost all cases will be to reduce the sensitivity of any subsequent test, especially with respect to the large molecules.
Further, unless the liquid sample collected on the receiving surface is drained from a defined sample volume and collected in a defined area, the results of a subsequent assay are unreferenced and cannot be compared over a period of time or from subject to subject. Again, the sensitivity of testing cannot be defined.
There are other difficulties in attempting to collect a liquid sample from a fecal specimen in conjunction with a guaiac test. In the use of devices such as that of Baker, the portion of the insert containing the liquid sample must be cut or punched from the insert, a process which requires unsanitary contact.
Another major problem with such devices is that they must sit for a substantial period of time before they are analyzed. Often, this involves transit through the mails, under a wide variety of ambient conditions of temperature and humidity. Sticking together of parts of the collection device is a major problem, as is drying and possible loss of portions of the specimen.
Such collections also risk the contamination of the liquid sample with wet guaiac indicator diffusing from the specimen receiving sheet. In addition, the device as disclosed and similar devices are complex and expensive to fabricate.
Immunological tests for hemoglobin are presently available in rapid, convenient, easily interpretable colorimetric form equivalent or superior in sensitivity to the guaiac test. Further, solid-phase immunoassays can concentrate analyte from dilute samples, thus achieving higher sensitivity than colorimetric chemistries. Such tests may be substituted for the guaiac test as a primary rather than confirmatory procedure if there is a means provided to obtain an appropriate liquid or semi-liquid sample from the fecal specimen. Also, in an immunological test for occult blood, just as in the guaiac test, a time lapse between the collection of the specimen and the hemoglobin assay does not affect the accuracy of the result. Accordingly, the design of a fecal specimen collecting device for occult blood testing directed only to the collection of an appropriate liquid fraction can be freed from the requirements and restrictions of the guaiac chemistry.
Devices which can collect fecal specimens for analysis without commitment to a defined chemistry can also be used to collect any semi-solid specimen in an analogous way. Such specimens can be blood clots, vomitus, sputum, pus, or solid tissue. The collected material can then be conveniently eluted and analyzed for a variety of substances according to appropriate analytical procedures, rather than restricted to an in situ colorimetric chemical analysis.
It is therefore an object of the invention to provide a device capable of collecting a liquid or semi-solid specimen and providing for convenient sampling therefrom.
Another object is to provide a convenient, sanitary, folding sample device that can be shipped through the mail or stored for a period of time with greatly reduced drying and sticking problems.
It is further an object of the invention to provide a device capable of collecting a sample of liquid from a semi-solid specimen wherein the sample accurately represents the native composition of the liquid.
It is also an object of the invention to provide a device capable of collecting a representative sample from a defined volume of the specimen.
It is further an object of the invention to provide a device which allows for the sanitary and convenient removal of a sample of the thus-collected specimens to a separate test device.
It is further an object of the invention to provide a procedure whereby a sample collected from a fecal specimen in the device of the invention is then analyzed for hemoglobin by a solid-phase enzyme immunoassay, and this procedure is a screening test for occult blood.
It is further an object of the invention to provide a device capable of conveniently collecting a representative sample from a liquid or semi-solid specimen, which device can be easily and inexpensively fabricated from a unitary blank.